The present invention relates to a semiconductor integrated circuit device and a process for producing the same. More particularly, the present invention pertains to a technique which may be effectively applied to a semiconductor integrated circuit device having a multilayer wiring structure and a process for producing such a semiconductor integrated circuit device.
Recently, it has been increasingly important to develop an effective technique of repairing a defective part in an LSI (Large Scale Integrated Circuit) or changing a logical design thereof by disconnecting and properly reconnecting part of the wirings within the LSI circuit after the completion of the LSI which is still in the form of a wafer or chip.
To attain the above-described object, the present applicant proposed in Japanese Patent Application No. 70979/1986 a method of connecting wirings in an LSI by a combination of an ion beam technique and a laser CVD technique. According to the proposed method, after the completion of an LSI having, for example, a double-layer wiring structure, wirings in a first-level layer are interconnected for the purpose, for example, of repairing a defective part or changing a logical design. In this case, since the wiring in the uppermost layer is generally widely laid out in order to supply a power supply current, it is necessary to provide contact holes extending through the wiring in the uppermost-level layer so as to reach the wirings in the lower-level layers and also provide a connecting wiring through the contact holes. For this arrangement, an insulating film on the uppermost-level wiring layer, the second-level wiring layer and an intermediate insulating film between the second-level wiring layer and the first-level wiring layer are processed by irradiation with a focused ion beam to form contact holes, thereby partially exposing the surfaces of the wirings in the first-level layer through the contact holes. After an insulating film, e.g., a silicon dioxide (SiO.sub.2) film, has been formed on the whole surface of the chip, this insulating film is patterned by the use of photolithography and etching techniques so that the insulating film is left only in the vicinities of the contact holes. Then, the insulating film on the bottoms of the contact holes are removed by selective etching so that the surfaces of the wirings in the first-level layer are partially exposed through the contact holes again. Then, a metal is selectively deposited by laser CVD to thereby form a connecting wiring which interconnects the wirings in the first-level layer through the contact holes. In this case, since the connecting wiring is insulated from the wiring in the second-level layer by the insulating films formed within the contact holes, the wirings in the first- and second-level layers are prevented from shorting to each other.
On the other hand, as the result of increases in the degree of integration and miniaturization of ICs, it has recently been increasingly important to conduct an operation in which a defective part of an LSI is debugged or repaired in the step of developing the same by disconnecting and properly reconnecting part of the wirings within the LSI chip, thereby detecting errors in design or process, carrying out a defect analysis and returning the LSI to the process conditions, and thus increasing the production yield. For this purpose, examples in which the wirings in ICs are disconnected by means of a laser or ion beam have heretofore been reported.
More specifically, as a first prior art, "Laser Stripe Cutting System for IC Debugging" (Tech Digest of CLEO' 81, 1981, p.160) is known. In this prior art, an example in which wirings are disconnected by means of a laser to debug a defective part is reported. As a second prior art, Japanese Patent Application No. 42126/1983 is known. This prior art discloses a technique in which an ion beam generated from a liquid metal ion source is focused in the shape of a spot having a diameter of 0.5 .mu.m or less to disconnect wirings and bore holes and a metal is deposited in the holes by an ion beam to thereby interconnect the upper and lower wirings.
As a third prior art, "Direct Wirting of Highly Conductive Mo Lines by Laser Induced CVD" (Extended Abstruct of 17th Conf. on Solid State Devices and Material, 1985, p.193) is known.